Laser machining apparatus

Abstract

A laser machining apparatus has a laser beam irradiation unit that includes: a pulsed laser oscillator that oscillates a pulsed laser beam at a given repetition frequency; first and second condensers that collect the pulsed laser beam oscillated by the pulsed laser oscillator; and a beam splitting unit arranged between the pulsed laser oscillator and the first and second condensers to split the pulsed laser beam oscillated by the pulsed laser oscillator and direct the resultant beams alternately toward the first and second condensers. The beam splitting unit includes a photoelastic modulator that has a piezo element and a synthetic quartz formed in one piece and modulates the laser beam so that a polarization plane of the laser beam is alternately at 0 and 90 degrees by applying, to the piezo element, a high frequency voltage at a frequency that matches the natural frequency of the synthetic quartz.

What is claimed is: 
     
       1. A laser machining apparatus comprising:
 chuck table operable to hold a workpiece; and 
 laser beam irradiation means operable to irradiate the workpiece held by the chuck table with a laser beam, 
 the laser beam irradiation means including
 a pulsed laser oscillator adapted to oscillate a pulsed laser beam at a given repetition frequency, 
 first and second condensers adapted to collect the pulsed laser beam oscillated by the pulsed laser oscillator, and 
 beam splitting means arranged between the pulsed laser oscillator and the first and second condensers to split the pulsed laser beam oscillated by the pulsed laser oscillator and direct the resultant beams alternately toward the first and second condensers, 
 the beam splitting means including a photoelastic modulator that has a piezo element and synthetic quartz formed in one piece and modulates the laser beam so that a polarization plane of the laser beam is alternately at 0 and 90 degrees by applying, to the piezo element, a high frequency voltage at a frequency that matches the natural frequency of the synthetic quartz. 
 
 
     
     
       2. The laser machining apparatus of  claim 1 , wherein
 the beam splitting means includes, from a side of the pulsed laser oscillator toward a side of the first and second condensers
 a first half wavelength plate, 
 a photoelastic modulator, 
 a second half wavelength plate, and 
 a polarization beam splitter, and wherein 
 
 when the frequency of the photoelastic modulator is denoted by f PEM , the repetition frequency of the pulsed laser oscillator by f Laser , and a natural number by m, the repetition frequency f Laser  is found by the following formula: 
 
       
         
           
             
               
                 f 
                 Laser 
               
               = 
               
                 
                   
                     
                       4 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       
                         f 
                         PEM 
                       
                     
                     
                       ( 
                       
                         
                           2 
                           ⁢ 
                           m 
                         
                         + 
                         1 
                       
                       ) 
                     
                   
                   ⁡ 
                   
                     [ 
                     Hz 
                     ] 
                   
                 
                 . 
               
             
           
         
       
     
     
       3. The laser machining apparatus of  claim 2 , wherein
 the natural frequency of a synthetic quartz is 50 kHz, and wherein 
 when f PEM =50 kHz and m=0, 1, 2, 3, 4 and so on are substituted, the repetition frequency of the pulsed laser oscillator is found as f Laser =200 kHz, 40 kHz, 8 kHz, 1.6 kHz, 320 Hz, and 64 Hz. 
 
     
     
       4. The laser machining apparatus of  claim 1 , wherein
 the beam splitting means includes, from a side of the pulsed laser oscillator toward a side of the first and second condensers
 a quarter wavelength plate, 
 a photoelastic modulator, 
 a half wavelength plate, and 
 a polarization beam splitter, and wherein 
 
 when the frequency of the photoelastic modulator is denoted by f PEM , the repetition frequency of the pulsed laser oscillator by f Laser , and a natural number by m, the repetition frequency f Laser  is found by the following formula: 
 
       
         
           
             
               
                 f 
                 Laser 
               
               = 
               
                 
                   
                     
                       2 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       
                         f 
                         PEM 
                       
                     
                     
                       ( 
                       
                         
                           2 
                           ⁢ 
                           m 
                         
                         + 
                         1 
                       
                       ) 
                     
                   
                   ⁡ 
                   
                     [ 
                     Hz 
                     ] 
                   
                 
                 . 
               
             
           
         
       
     
     
       5. The laser machining apparatus of  claim 4 , wherein
 the natural frequency of a synthetic quartz is 50 kHz, and wherein 
 when f PEM =50 kHz and m=0, 1, 2, 3, 4 and so on are substituted, the repetition frequency of the pulsed laser oscillator is found as f Laser =100 kHz, 20 kHz, 4 kHz, 800 Hz, 160 Hz, and 32 Hz.